Advanced wireless devices may have multiple radios that operate on the same, adjacent, or harmonic/sub-harmonic frequencies. The radios may provide access to networks such as a wireless wide area network (WWAN), a wireless local area network (WLAN), a wireless personal area network (WPAN), Global Positioning System (GPS), Global Navigation Satellite System (GLONASS), etc. Some combinations of radios may cause co-existence issues due to interference between the respective frequencies. In particular, when one radio is actively transmitting at or close to the same frequency and at the same time that another radio is receiving, the transmitting radio may cause interference to (i.e., de-sense) the receiving radio. For example, interference may occur between Bluetooth (WPAN) and 2.4 GH WiFi, (WLAN); adjacent band interference between 2.4 GHz WLAN and Long Term Evolution (LTE) band 7, 40, and 41; harmonic/sub-harmonic interference may occur between 5.7 GHz ISM and 1.9 GHz Personal Communications Service (PCS); and an intermodulation issue may occur between around 700 MHz and a GPS receiver.
FIG. 1 is a block diagram illustrating an exemplary analog interference cancellation system 100. Analog interference cancellation (AIC) cancels interference between a transmitter radio and a receiver radio by matching gain and phase of a wireless coupling path signal and in a wired AIC path, as shown in FIG. 1, where dt is a transmitted signal from a transmitter (aggressor) radio 102, and hc is a coupling channel (wireless or wired coupling path signal) from the transmitter radio 102 to a receiver (victim) radio 104. AIC 106 attempts to cancel the impact of the coupling channel hc as reflected via the negative sign on the output of AIC 106.
Interference cancellation techniques are commonly used in wireless communication systems to improve performance where undesired transmit interference (i.e., local interference) couples into a co-located receiver. In the case of a transmit antenna and a receive antenna, an analog interference cancellation (AIC) circuit in the receiver may be used to mitigate the undesired transmit interference by subtracting a filtered copy of the transmit interference (e.g., available from the transmitter) in the receive path to cancel the undesired transmit interference.